1. Field
This disclosure is generally related to MEMS (Micro Electro Mechanical Systems) technology assemblies, in particular a resonator assembly comprising two resonators, for example made of different materials such as a silicon resonator and a quartz resonator, for example suitable for use in an Inertial Navigation System.
2. Description of Related Art
Typically, an INS (Inertial Navigation System) in an aircraft consists of three angular rate sensors, three accelerometers, and GPS (Global Positioning System) made up electronic boards with custom ASICs (Application Specific Integrated Circuits), RF (Radio Frequency) hybrids, and commercial off-chip oscillators and filters. These components are packaged in multiple boxes which can be decoupled mechanically and thermally. An INS can in particular comprise a gyroscope and a clock.
It is known to make a gyroscope having a MEMS resonator, for example a High-Aspect-Ratio Si Resonator. A High Aspect Ratio structure as recited in the present application is a structure in which the height or thickness of the structure is much greater than lateral dimensions defined within, the structure. For example, a ring structure having a ratio height/gap spacing >2 for the rings is a High Aspect Ratio structure. An example of a High-Aspect-Ratio Si Resonator is a Si Disc Resonator Gyroscope (DRG) as described in U.S. Pat. No. 7,581,443, where the resonator layer is bonded to a Si substrate and then etched with deep reactive ion etching.
It is also known to make a MEMS quartz resonator for a quartz clock that can be bonded and integrated to a Si substrate, as described in U.S. Pat. No. 7,459,099.
U.S. Pat. No. 8,151,640 teaches using planar bonding techniques to first integrate a quartz clock resonator on a semiconductor substrate, followed by the integration of a High-Aspect-Ratio Si DRG Resonator on the substrate.
However, depending on the material used in the fabrication of the quartz resonator, the quartz resonator can be damaged or its frequency modified by the etching of the Si when forming the Si resonator. This is particularly important if the quartz resonator has Au electrodes as used commonly for HF and VHF shear-mode resonators.
There exists a need for an integrated structure comprising two resonators such that the fabrication of the later fabricated resonator does not detrimentally affects the properties of the earlier fabricated resonator.